Process of joining metals / alloys

The process performed by Heat with or without Pressure

Filler metal may or may not be used

The joint will be homogeneous

What Is Welding ?

Metal parts locally heated to melt along the joint.

Heating by oxy fuel flame or electric Arc.

Invariably filler metal added to molten pool.

On cooling, molten puddle solidifies to permanent homogeneous joint.

Fusion Welding Process

Shielded Metal Arc Welding- SMAW Gas Tungsten Arc Welding - GTAW Gas Metal Arc Welding - MIG / MAG Submerged Arc Welding – SAW Gas welding – Oxy Fuel Gas Electron Beam Welding - EBW Thermit Welding

Types Of Fusion Welding

Arc Welding

Arc welding dates back to the late 1800’s First developed following the invention of AC

electricity Pioneered when a man was welding with a bare

metal rod on iron, the sparks from the welding caught a stack of newspapers on fire near him and while welding, he noticed that his welds started looking a lot better. The reason for this was the smoke took the oxygen out of his welding environment and decreased porosity

History of Arc Welding

The fusing of two or more pieces of metal together by using the heat produced from an electric arc welding machine.

What is Arc Welding?

The arc is like a flame of intense heat that is generated as the electrical current passes through a highly resistant air gap.

How an arc is formed?

Shielded Metal Arc Welding- SMAW Gas Tungsten Arc Welding - GTAW Gas Metal Arc Welding - MIG / MAG Submerged Arc Welding – SAW

Welding Processes

Also referred to as “Stick Welding”

Used for everything from pipeline welding, farm repair and complex fabrication.

Uses a “stick” shaped electrode.

Can weld: steel, cast iron, stainless steel, etc.

SMAW

An electric Arc struck between electrode and base metal joint

Base metal melts under arc Electrode tip melts in drops

and transfers to molten pool of BM

Electrode with Arc moves along the joint keeping constant arc length

On cooling pool solidifies

SMAW

SMAW

SMAW

The equipment is relatively simple, inexpensive, and portable.

The shielding gas, provided by the burning flux, is less sensitive to wind and drafts when compared to processes with an external shielding gas.

It is very versatile. It can be used in limited access areas. It is suitable for most common metals and alloys. It is capable of producing high-quality welds. Deposition rates are higher than the gas tungsten

arc welding process

SMAW Advantages

Deposition rate is low compared to GMAW or FCAW.

Multiple stops required as a result of electrode length prevent continuity of filler deposition.◦ The weld is covered

by a layer of slag that must be removed after completion of welding.

SMAW Disadvantages

Electrode Identification

Breakdown of Electrode Identification SystemE7018: E-Electrode, 70-Strength, 1-Position,

8-Coating

• Also referred to as “TIG” Welding

• Uses a shield gas, a non-consumable tungsten electrode and a hand fed filler rod

• Excellent for welding thin metals, pipeline welding and exotic metals

• Highly skilled labor needed for this process

GTAW

GTAW

GTAW

Capable of welding thin material. Controls heat input extremely well because the

heat source and the filler material are separately controlled.

Welds can be made without adding filler material by fusing the base metals together.

Full penetration welds that are welded from one side only can be made.

Capable of producing defect-free welds. Recommended for materials that form

refractory oxides, like aluminum and magnesium.

GTAW Advantages

Cost of equipment and shielding gas is high. Deposition rate is slow. A high degree of operator skill is required to

produce quality welds. Fit-up tolerances are restrictive. Exposure to hot filler material with the

atmosphere through mishandling can cause weld metal contamination.

GTAW Disadvantages

Gas Metal Arc Welding, or MIG uses an electric arc between a continuous feed of filler metal (wire) to produce heat input.

Shielding is obtained entirely from an externally supplied gas or gas mixture

This type of welding can operate in manual,

automatic, or semi automatic modes of operation.

Gas Metal Arc Welding orMetal Inert Gas (MIG)

Gas Metal Arc Welding orMetal Inert Gas (MIG) Wire Feed MIG = Metal Inert Gas

◦ Inert Gas= Inactive gas that does not combine chemically with base or filler metal

MAG= Metal Active Gas◦ Active Gas= Gas will combine chemically with

base or filler metal

Deposition rate is high.

Costs are low because there is less electrode waste, no slag removal and welder down-time due to changing electrodes is less compared to SMAW.

Smoke and fumes are minimal.

Obtains deeper penetration than SMAW or GTAW.

It is very versatile (all position process for carbon, low alloy and stainless steels).

MIG Advantages

Cost of machinery, shielding gas, and maintenance is high.

Accessibility to welding joint can be restrictive due to the size of the gun.

Shielding gas is sensitive to wind and drafts.

The length of a welding arc is restrictive.

The equipment is not as portable as SMAW.

MIG Disadvantages

Electrode Identification

Breakdown of Electrode Identification SystemER70S-X; ER-Electrode Rod, 70-Strength, S-Solid Wire,

X-Chemical Composition

MIG

Flux cored arc welding uses the heat of an arc between the continuous filler metal electrode and the work piece (as in GMAW) to create the necessary input heat.

However, shielding is obtained, in whole or part, by flux contained within the tubular electrode.

Self shielding electrodes require no external gas protection, while other flux-cored electrodes use additional external gas shielding.

Flux Core Arc Welding (FCAW)

Flux Core Arc Welding (FCAW)

Flux Core Arc Welding (FCAW)

FCAW Electrode Classification

E70 T - 1Electrode

Minimum UTS70,000 psi

Position

Flux Cored /TubularElectrode

Type Gas, Usabilityand Performance

American Welding Society SpecificationAWS A5.20 and AWS A5.29.

Deposition rate is high. Cost are low because there is

less electrode waste. Welder down-time is less due

to continuity of welding One can utilize economical

joint designs. Compared to SMAW,

distortion of the material is less.

Excellent profile for horizontal fillet welds.

FCAW Advantages

Cost of machinery and maintenance is high.

Electrode is more expensive than GMAW

Length of welding arc is restrictive.

Not as portable as SMAW.Produces more smoke and

fumes than GMAWSlag covering must be

removed.

FCAW Disadvantages

The submerged arc welding process is similar to the gas metal arc welding process except the arc is struck under a blanket of granular flux, hence the name submerged arc welding.

The filler metal is a continuously-fed wire electrode like GMAW and FCAW. However, higher deposition rates can be achieved in SAW by using larger diameter electrodes (up to 1/4”) and higher currents (650-1500 Amperes).

Since the process is almost fully mechanized, several variants of the process can be utilized such as multiple torches and narrow gap welding.

Submerged Arc Welding

Submerged Arc Welding

Submerged Arc Welding

High deposition rates No arc flash or glare Minimal smoke and fumes Flux and wire added

separately - extra dimension of control

Easily automated Joints can be prepared with

narrow grooves Can be used to weld carbon

steels, low alloy steels, stainless steels, chromium-molybdenum steels, nickel base alloys

Advantages

Flux obstructs view of joint during welding

Flux is subject to contamination Þ porosity

Normally not suitable for thin material

Restricted to the flat position for grooves - flat and horizontal for fillets

Slag removal required Flux handling equipment

Limitations